Nonaqueous electrolyte secondary batteries such as lithium ion secondary batteries have various advantages like high energy density, small self-discharge and excellent long-term reliability, and are already commercialized by virtue of such advantages as batteries for notebook personal computers or cellular phones. However, in recent years, since electronic devices are equipped with higher functions and the use of electronic devices for electric cars is advancing, the development of lithium ion secondary batteries having higher energy density is underway.
On the other hand, the higher the energy capacity or the energy density of a battery becomes, the more likely the battery temperature is to rise when a short circuit occurs due to an impact from outside or a circuit failure or when the battery is overcharged. At this time, oxygen desorbing reaction of an active material or thermal decomposition reaction of an electrolyte occurs, which causes the battery to further generate heat.
Conventionally, various interrupting mechanisms have been disclosed as solutions to heat generation of batteries. For example, Patent Literature 1 discloses a battery structured such that a thin plate is provided inside a housing, which is deformed when an inner pressure increases and part of an electrode lead is welded to the thin plate. In such a configuration, deformation of the thin plate caused by an increase in the inner pressure causes the electrode lead to be cut and current is thereby interrupted. Patent Literature 2 discloses that a compound which is oxidized at a predetermined voltage or higher is added to an electrolyte. By heat generation at the time of oxidation, this compound induces decomposition of components of the electrolyte or vaporization, causes the inner pressure of the battery to increase, and the pressure increase activates safety means to effectively function. Patent Literature 3 discloses an interrupting mechanism with a heat fuse incorporated into a current output conductor. Patent Literature 4 discloses an interrupting mechanism having a structure in which a battery case that houses an electrode assembly is made expandable in a direction in which an electrode lead is led out, the battery case expands when an inner pressure of the battery increases and a joint between the electrode lead and an electrode tab is separated.
Patent Literature 5 discloses a battery having a structure in which a battery case that houses an electrode assembly is formed of a bag of a heat sealable film and an interior of the bag is divided into a main chamber that houses the electrode assembly and a sub-chamber adjacent to the main chamber, and through which an electrode lead passes. A partition sealing section that partitions the main chamber from the sub-chamber includes a weak sealing section. Inside the sub-chamber, the electrode lead is provided with an interrupting mechanism whereby the electrode lead is disconnected when an inner pressure increases. According to the battery in such a configuration, when an inner pressure in the main chamber increases due to the occurrence of abnormality, the weak sealing section is opened, the sub-chamber inflates and the electrode lead is thereby disconnected.